Computational chemistry: Modeling of polymer degradation by atomic oxygen in low Earth orbit

The space shuttle, the international space station (ISS), and many other satellites travel around the Earth through the space region called low Earth orbit (LEO), the altitudes of 180 to 650 kilometers above the Earth's surface. The largest component of the atmosphere at these altitudes is atomic oxygen (AO), which is created when oxygen molecules are split by short wavelength solar ultraviolet radiation. Oxygen atoms hit the surface of orbiting spacecraft with impact energies of ∼100 kcal/mol. Spacecraft surface materials particularly affected by AO are organic polymers, which lose weight, and depending on thickness can be eroded away completely.; Knowledge of the long-term durability of materials exposed to AO in the LEO environment is crucial to numerous space missions and experiments. Despite enormous experimental efforts during the past two decades, to date there is no clear understanding of mechanisms for materials interaction with AO. Therefore, the ability to predict how a certain material would behave in LEO environment is very limited.; In this work we employ computational chemistry techniques in order to elucidate plausible mechanisms of various organic polymers degradation by AO. Molecular fragments that are present in the repeat units of the polymers serve as models of these materials. Activation energies for the reactions of the model molecules and AO are computed with the use of ab initio methods. Low activation energies are found for molecular fragments present in many materials, which offers an explanation for relatively high measured erosion rates of those materials.